A micro carbon material such as carbon black, Ketjen black, fullerene, graphene or carbon nanotubes has been widely used in energy, aerospace fields, etc. because of excellent electrical characteristic and thermal conductivity. However, while to apply these micro carbon materials, uniform dispersion should be preceded, it is difficult to prepare a high concentration dispersed liquid of such a micro carbon material by a conventional method such as mechanical dispersion, dispersion using a dispersing agent, or dispersion through surface functionalization.
Recently, according to the technical development and increased demand for mobile devices, the demand for secondary batteries as an energy source is dramatically increasing. Among these secondary batteries, a lithium secondary battery which has higher energy density and voltage, a longer cycle lifespan and a lower self-discharge rate has been commercialized and widely used.
In a lithium secondary battery, electrodes including a positive electrode and a negative electrode are manufactured by mixing an electrode active material and a binder with a solvent in a batch to prepare a composition for forming an electrode, and applying the prepared composition for forming an electrode to a collector, followed by drying the composition. Here, to ensure conductivity between the active material and the collector, the composition for forming an electrode may include a fine carbon-based conductive material, and among these materials, carbon black has been widely used in that an active material charging rate can be increased, and the increase in internal resistance of the battery can be suppressed even in a small amount thereof.
However, since a conductive material is used in the form of several tens of nanometer-scale fine particles, they have a high cohesive strength, and therefore when dispersed in a solvent, aggregation between conductive material fine particles easily occurs. Such non-uniform dispersion of the conductive material in an electrode active material layer results in the decrease in conductivity and output characteristic of the battery, and an aggregate prepared by simply aggregating the conductive material has low structure maintenance, conductivity between active materials may be degraded. In addition, the conductive material may cause the non-uniform distribution of the binder in the active material layer and a decrease in the adhesive strength by adsorbing the binder due to a large specific surface area.
Therefore, by a method of preparing a paste by previously dispersing a conductive material in a solvent together with binder, and then adding an electrode active material to the paste, followed by stirring and mixing the resulting mixture, it was intended to solve problems associated with the dispersion of the conductive material. However, a dispersed liquid including a resin-based binder such as a fluorine resin, a cellulose resin, etc. may not have sufficient effects because of poor dispersion stability of conductive material particles and reaggregation of the conductive material particles.
In addition, there was an attempt to increase dispersibility of a conductive material by adding a vinyl pyrrolidone-based polymer as a dispersing agent to a conductive material and a solvent, and thereby, to favorably maintain a load characteristic or cycle characteristic of a battery. However, in this case, an electrode active material was insulated with the added vinyl pyrrolidone-based polymer by coating, or the added vinyl pyrrolidone-based polymer was modified to degrade a discharge characteristic when the battery is stored for a long time while charged, resulting in degradation in battery characteristics.
For the expansion of use of micro carbon particles in various fields as well as the lithium secondary battery, it is necessary to develop a method of uniformly dispersing micro carbon particles.